Preparation of 1, 3-butylene glycol



April 2z, 1947.

l. L. woLK PREPARATION 0F l 5BUT-YLENE GLYvCOL Filed Dec. 14, 1952JOD... OP

.zormzunzou Patented pr. 22, 1947 PREPARATION 0F LS-BUTYLENE GLYCOL I.Louis Wolk, Bartlesville, Okla., assigner to Phillips Petroleum Company,a corporation of Delaware Application December 14, 1942, Serial No.468,959

2 claims. l

This invention relates to an improved process for the preparation of1,3-butylene glycol from ethyl alcohol as a starting material. As is nowwell-known, butylene glycol may he readily dehydrated to form butadienewhich is employed as a monomeric raw material in the preparation ofsynthetic rubber. Accordingly, 1,3-butylene glycol is a very importantchemical compound and its ready and economical preparation from amaterial as cheap and readily obtainable as ethyl alcohol assumes greatimportance.

The principal object of the present invention is to provide an improvedprocess for the production of 1,3-butylene glycol from ethyl alcohol.Another object is to devise such a method involving electrochemicalsteps in an integrated relationship. Another object is to provide such aprocess involving electrochemical steps wherein substantial savings inpower are effected along withv other improvements, since one of theprincipal objections to ordinary electrolytic organic reactions is therelatively large cost of power consumed in carrying out the electrolyticreaction. Another object is to simultaneously carry out one step oi theintegrated Process in the anode compartment of a divided electrolyticcell and another step in the cathode compartment of the same cell.Numerous other objects and advantages of the present invention will beat once apparent to those skilled in the art in the light of thisdisclosure.

The accompanying drawing, Iwhich is self-explanatory, portraysdiagrammatically one embodiment of the present invention.

In accordance with my invention, ethyl alcohol is oxidized toacetaldehyde in the anode compartment of an electrolytic cell, theacetaldehyde so formed is condensed to aldol, and the aldol is reducedt-o 1,3-butylene glycol in the cathode compartment of an electrolyticcell, preferably of the same cell as that in which the acetaldehyde isformed. By simultaneously carrying out the oxidation of the startingethyl al-- cohol to acetaldehyde and the reduction of the aldol toLil-butylene glycol in the anode and cathode compartments respectively,of one and the same electrochemical cell, great -ec0nomies andconvenience of operation are effected and the same electric current isused for both the electrolytlc oxidation and reduction whereby -verygreat savings in power cost are attained. The condensation of theacetaldehyde to aldol may conveniently be carried out in a separatestep. Methods of effecting this condensation are welk-known vto the art,as illustrated by U. 'S.

2 Patents to Earle et al., 1,094,314; Grunstein, 1,437,139; Matheson,1,450,984; and Mueller- Cunradi et al., 1,881,853. However, since thecondensation of acetaldehyde to aldol may take place in an alkalinealcoholic aqueous solution, this condensation may be-effected in thecompartment of thecell wherein the acetaldehyde is formed from the ethylalcohol, by utilizing an alkaline electrolyte for the oxidation of theethyl alcohol, unreacted alcohol serving to render the anolytealcoholic. If desired or necessary, the effluent from the anodecompartment may be introduced into a receptacle and maintained atcondensation temperature for the required period of time to completecondensation of the acetaldehyde to aldol. The aldol solution containingalkali, unreacted alcohol and possiblysome uncondensed acetaldehyde maythen be introduced into the cathode compartment of the same electrolyticcell where the aldol is reduced vto 1,3- butylene glycol. If desired,the aldol-containing solution may be treated in any known manner toconcentrate the aldol content thereof prior to introduction of the aldolto the cathode compartment wherein it is reduced to butylene glycol.

Likewise, the acetaldehyde-containing anolyte removed from the anodecompartment in which the acetaldehyde is formed may be treated in anysuitable manner, if desired, to concentrate the acetaldehyde prior toits introduction to the unit or zone in which it is condensed to aldol.

The electrochemical oxidation of ethyl alcohol to acetaldehyde in theanode compartment is a matter well within the skill of the art and theselection of anolyte composition, temperature, anode, current densityand other conditions of this operation will be obvious to those skilledin the art in the light of this disclosure taken in conjunction with theprior art. Accordingly, speciilc conditions need not be given here indetail.

Ordinarily a current of 3-6 amperes/square decimeter and 3-15 volts willprovide suitable current conditions for both the anodic and cathodioreactions described herein.

In many cases it will be desirable to carry out the oxidation of theethyl alcohol to acet'aldehyde in an acid anolyte since under manycircumstances use of an acid electrolyte, for eX- ample, dilute sulfuricacid, favors the production of acetaldehyde as the principalor mainproduct, as is well known to the art. However, the use of an alkalineelectrolyte in the anolyte is not precluded and may bedesirableespecially where the same divided cell is used forltheproduction of the acetaldehyde and for the reduction of the aldol andwhere an alkaline cletrolyte in the catholyte is used. As pointed outabove, such use of an alkaline anolyte may be especially desirable wherepartial or complete condensation of the acetaldehyde to aldol in theanode compartment is sought.

The reduction of the aldol to 1,3-butylene glycol is carried out in thecathode compartment of an electrolytic cell. Here again the selection ofconditions and materials is well within the skill of those versed in theart, this reduction per se being well disclosed in the literature astypied by the U. S. Patents to Earle et al., 1,094,315 and 1,094,316;and Delbruck et al., 1,094,539. This reduction may be conducted witheither an alkaline or an acid catholyte. Where the catholyte containsalkali metal ions, such as sodium,

it is especially desirable to use a mercury or an amalgamated metalcathode on the surface of which sodium amalgam forms. Alternatively,r Imay use a cathode of platinum, palladium, nickel, iron, copper, zinc,tin, lead, or other metal having catalytic properties for the reaction.Noncatalytic cathodes may aise be used since nascent hydrogen is anactive reducing agent.

Following reduction in the cathodey compartment the catholyte is treatedin any suitable manner to recover the 1,3-butylene glycol contentthereof. present in the catholyte is reconverted to ethyl alcohol, andthe ethyl alcohol so formed may be separated from the butylene glycol bydistillation and recycled. It is preferred to recover essentially purebutylene glycol Where, as ordinarily, it is to be used as a chemicalintermediate, for example, as a starting material for the preparation ofbutadiene.

A batch process may be used. At least the electro-organic oxidation andreduction steps may be conducted batchwise since they may not lendthemselves too readily to truly continuous operation. However,continuous operation may be employed throughout if desired. In such casea series of cells may be utilized in order to provide a longer residencetime.

It will be understood that while operation with simultaneous oxidationto acetaldehyde and reduction to butylene glycol in anode and cathodecompartments, respectively, of the same cell, is highly preferred, I amnot limited thereto but may carry out these steps in different cells, asfor example, where it is desired to use conditions' for one of thereduction and oxidation steps which would be incompatible with theconditions desired for the other of said steps. Such conditions mightinvolve temperature, electrolyte composition, voltage, current, time,etc.

Almost invariably it is preferred that divided cells be used for boththe oxidation and the reduction in order to prevent the oxidationproducts from being reduced at the cathode and the reductionr productsfrom being oxidized at the cathode, to preclude other undesirableeffects, and to keep the anolyte and catholyte separate. The selectionof a suitable diaphragm for this purpose is well within the skill of theart.

As will be obvious, I may periodically or continuously during theelectrolysis adjust the composition of anolyte or. catholyte or both inany desiredy manner, for example, by addition of a neutralizing acidicor acid-forming or a basic or base-forming material in suitable amountto prevent the building up of an excessive acidity or alkalinity.

Any uncondensed acetaldehyde It will be understood that where a singlecell is used, the oxidation being conducted in the anode compartment andthe reduction being carried out in the cathode compartment, theconditions for each will have to be so selected as to be compatible withone another. This is especially true of the electrolyte. Thus both theanolyte and catholyte may be either acid or alkaline in reaction, or onemay be acid and the other alkaline, provided other conditions areadjusted accordingly. If desired I may use an electrolyte containing asalt such as an alkali sulfate, for example, sodium sulfate, wherebysulfuric acid is continuously formed in the anolyte and maintains itacid while alkali hydroxide is formed in the catholyte. In this way,especially in the preierred embodiment involving simultaneous oxidationin the anode compartment and reduction in the cathode compartment of thesame cell, the oxidatio-n of the ethyl alcohol to acetaldehyde isconducted in an acid anoiyte which may be especially desirable where itis sought to produce acetaldehyde in maximum yield and to minimize sidereactions such as polymerization, etc., while the reduction of aldol tobutylene glycol is carried out in an alkaline catholyte which isfrequently very desirable. Of course free sulfuric acid may be used asan initial componemL of the anolytewhen such a salt is used, if desired.

In some cases it may be desirable to use an alkali carbonate as anelectrical conducting salt in the anolyte and catholyte. In such casethe acetaldehyde formed in the anolyte may be largely or completelycondensed to aldol as it is formed, since alkali carbonate is awell-known catalyst for aldol condensation. The withdrawn anolyte withor without additional treatment steps such as adjustment of composition,partial neutralization, concentration of aldol, a separate condensationstep to complete condensation of the acetaldehyde to aldol, may then bepassed to the cathode compartment where reduction to butylene glycoltakes place especially well in the presence of alkali carbonate. Insteadof alkali carbonate, the bicarbonate may be used. Likewise, if desired,carbon dioxide may be intermittently or continuously passed into thecatholyte to keep the alkalinity therein from becoming excessive.

In many cases it will be desirable to carry out the electrolyticreduction of the aldol to the 1:3 butylene glycol in the presence ofdilute sulfuric acid. An especially desirable mode of operation is touse a common divided cell and a common electrolyte, nameiy, dilutesulfuric acid in both anode and cathode compartments, whereby theoxidation of the ethyl alcohol is done in a sulfuric acid anolyte whichfrequently gives maximum yields of acetaldchyde and eliminatescondensation thereof to aldol or other reactions which would occur in analkaline anolyte, and whereby the reduction cf the aldol (which isproduced by condensation of the acetaldehyde in a separate unit apartfrom the cell) to butylene glycol takes place in a sulfuric acidcatholyte.

The electrolytic oxidation and reduction steps of the process of thepresent invention, and especially the reduction, are ordinarily andpreferably carried out at low temperature, i. e., at below roomtemperature (commonly taken as 20 C.). Generally temperatures not abovelo C. and varying downwardly therefrom to the freezing point of theelectrolyte are employed. Useof such low temperatures promotes thedesired reactions to a maximum and minimizes objectionable sidereactions, polymerization, formation of resins,

Example An alcoholic aqueous solution containing 10% water and 90% ethylalcohol to which solution has been added about 4% NaOH, is introducedinto the anode compartment of an electrolytic cell separated from thecathode compartment by a porous clay diaphragm. Initially, the sameelectrolyte may be placed in the cathode compartment. The electrolyte issubjected to electrolysis using a carbon anode and a current density ofamperes/square decimeter at a voltage of 6 volts. The electrolysis isconducted at a temperature of about 10 C. with stirring for a suicientlength of time to eectsubstantial conversion of ethyl alcohol toacetaldehyde, along with at least partial condensation of acetalde-`hyde to aldol, say Zelt) hours. The resulting electrolyte containingethyl alcohol, water, NaOH, aldol and acetaldehyde, is then introducedinto the cathode compartment of the cell using an amalgamated leadcathode and the same current conditions as in the anode compartment.v

The aldol is reduced to 1,3-butylene glycol, while residual acetaldehydeis re-converted to ethyl alcohol. Simultaneously, a fresh quantity ofalkaline aqueous ethyl alcohol is being oxidized in the anodecompartment. The catholyte is distilled after reduction to separate theglycol from the ethyl alcohol and water; which may be recycled to theanode compartment, after wash ing to remove alkali, substantially pure1,3- butylene glycol is obtained.

The above example describes a batch operation. If it is desired tooperate in a continuous manner, the anolyte iiows continuously throughthe anode compartment while being oxidized and may then ow eitherthrough a storage zone where the acetaldehyde will have a sufficientresidence time to complete condensation to aldol, or where the aldolformation has taken place in the anode compartment, may flow directlyinto and through the cathode compartment. In order to increase reactiontime the major portion of the electrolyte in each cell may becontinuously recycled, or a series of cells in parallel may be used.

Similar operating conditions are used with other electrolytes, such assulfuric acid or sodium sulfate, except that where the oxidation of thealcohol takes place in an acid medium, the electrolyte must beneutralized after oxidation and made alkaline in order that the aldolcondensation may take place in an alkaline medium.

The alcohol concentration in the anolyte may Vary over a wide range;ordinarily 50-95% alcohol is suitable. When an alkaline solution isdesired, alkali concentrations corresponding to 1-10% or more of NaOHmay be used. Where electrolytes acidied with acids, such as sulfuricacid, are used, the acid concentration may desirably be from 5-15%.

A great many advantageous featuresof the process of the presentinvention will be apparent to those skilled in the art. Among these, thefollowing may be enumerated. The most important advantage is that theinvention accomplishes production of very valuable 1,3-butylene glycolin a simple and economical manner from ethyl alcohol. Yields in eachstep, and consequently, the overall yield, are very good -The in-Vention permits utilization of the same electric power for both theoxidation and the reduction step. It conducts both oxidation andreduction in the same electrolyte. It permits at least partialcondensation of the acetaldehyde in the oxidation zone. It eliminatesthe necessity for separation of the aldol prior to the reduction step.It eiiects reconversion in the cathode compartment of unreactedacetaldehyde to alcohol which may then be recycled. It makes possible asemicontinuous or even a continuous method. Recycle of unreactedmaterials is readily accomplished and to a maximum extent whereby yieldsare improved.

I claim:

1. The process of making 1,3-butylene glycol from ethyl alcohol whichcomprises introducing an alcoholic aqueous solution containing 10% waterand 90% ethyl alcohol to which about 4% NaCl-l has been added into theanode compartment of an electrolytic cell having its cathode compartmentseparated from its anode compartment by a porous diaphragm, subjectingsaid solution to electrolytic oxidation at a carbon anode in said anodecompartment with a current density of 5 amperes per square decimeter at6 volts and at a temperature of about 10 C. with stirring for a lengthof time of from 2-10 hours suilicient to eiect substantial conversion ofethyl alcohol to acetaldehyde by electrolytic oxidation and simultaneouscondensation of said acetaldehyde to aldol in said anode compartment,introducing the resulting electrolyte containing ethyl alcohol, water,NaOH, aldol and acetaldehyde into the cathode compartment of the samecell, and subjecting said electrolyte to electrolytic reduction thereinat an amalgamated lead cathode under the same current conditions as inthe anode compartment and thereby reducing-said aldol to 1,3-butyleneglycol at said cathode and re-converting said acetaldehyde to ethylalcohol, simultaneously oxidizing a fresh quantity of said aqueousalkaline ethyl alcohol solution in said anode compartment, maintainingthe anolyte and catholyte separate during the process by means of saiddiaphragm, withdrawing the catholyte from said cathode compartment afterreduction of said aldol to 1,3-butylene glycol therein, separatelyrecovering the 1,3-butylene glycol in substantially pure form and theethyl alcohol from the catho-lyte, and recycling said ethyl alcohol tothe anode compartment.

2. The process of making 1,3-butylene glycol from ethyl alcohol whichcomprises introducing an alcoholic aqueous solution containing from to95 per cent ethyl alcohol to which solution has been added about 4% NaOHinto the anode compartment of an electrolytie cell having its cathodecompartment separated from its anode compartment by a porous diaphragm,subjecting said solution to electrolytic oxidation at a carbon anode insaid anode compartment with a current density of 3 to 6 amperes persquare decimeter at 3 to l5 volts and at a temperature of about 10 C.with stirring for a length oi time of 'from 2-10 hours sufcient toeffect substantial conversion of ethyl alcohol to acetaldehyde byelectrolytic oxidation and concomitant condensation of saidacetalydehyde to aldol in said anode compartment, introducing theresulting elec trolyte containing ethyl alcohol, water, NaOH, aldol andacetaldehyde into the cathode compartment of the same electrolytic cell,subjecting said electrolyte to electrolytic reduction therein at anarnalgamated lead cathode under the same range of current conditions asin the anode compartment and thereby reducing said aldcl to l,3bui.yleneglycol at said cathode and recon- Verting said acetaldehyde to ethylalcohol, simultaneously oxidizing electrolytically a fresh quantity ofsaid aqueous aikaline ethyl alcohol solution in said anode compartmentat the foregoing conditions, maintaining the ariolyte and catholyteseparate during the process by means of said diaphragm, withdrawing thecatholyte from said cathode compartment after reduction o said aldol to1,3-butylene glycol therein, separately recovering the 1,3-loutyleneglycol in substantially pure form and the ethyl alcohol from thecatholyte, and recycling said ethyl alcohol to the anode compartment.

I. LOUIS WOLK.

REFERENCES crrao The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,094,315 Earle et al. Apr. 21,1914 1,094,224 Kyriakdes et al. Apr. 21, 1914 1,094,559 Delbruck et alApr. 28, 1914 1,544,357 Thatcher June 20, 1925 1,885,242 Durians Nov. 1,1932 FOREIGN PATENTS Number Country y Date 140,115 British Mar. 25, 1920OTHER REFERENCES Muller, article in Zeitschrift fur Chemie, vol. 27, p.564 (1921).

Glasstone etal., Electrolytic Oxidation and Reduction, publ. 1936 by D.Van Nostrand Co.

Stscherbakow et al., article in Zeitschrift fur 20 chemie, v01. 35, pp.826-830 (1929

